The present invention relates to a skin pattern feature extracting apparatus for skin pattern images such as fingerprints, palmprints or ridge pattern of other parts of the body.
Skin patterns such as fingerprints or prints of other parts of the body (hereinafter represented by fingerprints), have features that they are "unique for each person" and "stay the same for his/her life time". Owing to these features of fingerprints, systems have been proposed and implemented for actual use, in which features of a scanned fingerprint image, such as shapes of ridges and positional relations of end points and bifurcations of the ridges known as minutiae, are extracted and matched with reference to enrolled fingerprint features for identifying persons. These systems are highly reliable. To obtain high identification accuracy in these systems, it is necessary to accurately extract positions of end points and bifurcations of ridges from the image.
However, by extracting the above features from the given scanned fingerprints, particularly those having poor quality for such reasons, as that it is a latent fingerprint, in an automated process, it is impossible to realize sufficient accuracy of identification. Therefore, it is necessary that an operator having rich experience displays a fingerprint image, having been read out by a scanner and digitized, on a display screen and input or correct with a mouse or like input means, positions of minutiae, which had not been able to be extracted or erroneously extracted in the automatic process. To support this operation, a "Fingerprint Feature Extraction Apparatus" is disclosed in Japanese Patent Laid-Open Publication No.5-35856. The disclosed apparatus has such functions as:
cutting out an instructed part from an input image including a fingerprint; PA1 subjecting the instructed part to an image enhancing process; and PA1 correcting feature extraction according to instructions.
The images before and after the processes are displayed, thus permitting the above manual feature extraction to be supported. By using this apparatus, the operator does operations of "manual plotting", i.e., manually inputting position and direction data of end points and bifurcations by watching the display, and "manual tracing", i.e., manually tracing ridges and inputting the traces.
In many cases of the above manual feature extraction from fingerprints and prints of other parts of the body, when the image as the input image is poor in quality in that it is a latent fingerprint, when the imprint area of the finger print image is small, or when many wrinkles are superposed on an image of a hand skin pattern print image, ridge traces and minute features of end points and bifurcations of the ridges are mixed with noise and can not be clearly observed by the operator. FIG. 7 shows an example of such an image. In this case, although it is clearly seen that ridges extend together substantially in the horizontal direction, it is considerably difficult to determine the positions of end points and bifurcations. For this reason, even a skilled operator may make person identification with reduced accuracy due to position errors.